Optimization of Protein Kinase CK2 Inhibitors Derived from 4,5,6,7-Tetrabromobenzimidazole

Abstract

Casein kinase 2 (CK2) is a ubiquitous, essential, and highly pleiotropic protein kinase whose abnormally high constitutive activity is suspected to underlie its pathogenic potential in neoplasia and infective diseases. Thus, CK2 inhibitors designed to dissect the signaling pathways affected by this kinase, in perspective, may give rise to pharmacological tools. One of the most successful CK2 inhibitors is TBB (4,5,6,7-tetrabromobenzotriazole). Here we show that its inhibitory properties can be markedly improved by generating adducts in which N(2) is replaced by a carbon atom bound to a variety of polar functions. The most efficient inhibitor is 4,5,6,7-tetrabromo-2-(dimethylamino)benzimidazole (2c) followed by the methylsulfanyl (8), isopropylamino (2e), and amino (2a) congeners. All these compounds display K(i) values <100 nM (40 nM in the case of 2c). 2c induces apoptosis of Jurkat cells more readily than TBB (DC(50) value 2.7 vs 17 microM) and, unlike TBB, it does not display any side effect on mitochondria polarization up to 10 microM concentration. Molecular modeling of the CK2-2c complex, based on the crystal structure of the CK2-TBB complex suggests that a number of additional apolar contacts between its two methyl groups and hydrophobic residues nearby could account for its superior inhibitory properties. Consequently, 2c is even more susceptible than TBB to mutations of the unique hydrophobic residues V66 and/or I174 to alanine. We propose to adopt 2c as first choice CK2 inhibitor instead of TBB, especially for in cell studies.

Modulation of extracellular matrix protein phosphorylation alters mineralization in differentiating chick limb-bud mesenchymal cell micromass cultures

“…There may also be effects of blocking CK2 on such events. Before chondrocyte nodules are formed, inhibitors that block phosphorylation affect cell viability, mitosis, chondrocyte condensation, and the cytoskeleton [33][34][35][36][37]. Thus phosphorylation and dephosphorylation play major roles in regulating the differentiation and proliferation of mesenchymal cells in culture, hence the studies reported here focused on times after the cells had differentiated and the matrix was formed.…”

“…Kinase and Phosphatase Activities-To define concentrations of inhibitors for analysis, a series of pilot experiments were performed in which a wide range of concentrations for each inhibitor starting with those reported in the literature [18,21,[33][34][35][36][37] were added either continuously from day 5, 7, 9 or 11, or once (acutely) at day 5,7,9,11, or 14. Where treatments caused visible cell death and cultures lifted off the culture dish no further analysis was done.…”

Pharmacological inhibition of protein kinase CK2 reverts the multidrug resistance phenotype of a CEM cell line characterized by high CK2 level

“…TBB was synthesized as in Szyszka et al (1995), IQA as in Sarno et al (2005), TBI and 2a as in Pagano et al (2004);and MNA and MNX as in De Moliner et al (2003).…”

CX-4945, an Orally Bioavailable Selective Inhibitor of Protein Kinase CK2, Inhibits Prosurvival and Angiogenic Signaling and Exhibits Antitumor Efficacy

“…Several research groups have reported that inhibition of CK2, either by siRNA directed toward CK2a (22) or by using chemical CK2 inhibitors such as 4,5,6,7-tetrabromobenzotriazole (23) and 2-(dimethylamino)-4,5,6,7-tetrabromo-1H-benzimidazole (24), induced apoptosis and prevented the proliferation of cancer cells. Furthermore, antisense oligonucleotides directed toward CK2a have been shown to induce apoptosis and exhibit antitumor activity in xenograft models (22,25).…”